The following symbols will have the following meanings in the description of the preferred battery testing system embodying this invention:
I(full) Maximum current applied to battery. PA1 M(t) Multiplier to adjust current down for a lower battery temperature. PA1 M(c) Multiplier to adjust current down for a lower battery charge. PA1 I(adj) Equal to I(full) times M(t) times M(c). PA1 R(adj) Battery resistance adjusted to full charge and 70.degree. F. PA1 R(bat) The actual resistance of the battery. PA1 CCA Cold Cranking Amps of a fully charged battery. PA1 V(d) Voltage drop across the battery due to an internal resistance and an applied current. PA1 CA Cranking Amps, the current that the battery can supply for 30 seconds at full charge and at 70.degree. F. and not drop the battery voltage below 1.2 volts per cell. PA1 AA Available Amps, the current the battery can supply for 30 seconds at the actual charge and temperature and not drop the battery voltage below 1.2 volts per cell. PA1 AH Amp Hours, the current in amperes times the number of hours to discharge. PA1 V(bat) The terminal voltage of the battery.
Cold Cranking Amps (CCA) are defined by the Battery Council International (BCI) as "the number of amperes a battery at 0.degree. F. (-17.8.degree. C.) can deliver for 30 seconds and maintain, at least, a voltage of 1.2 volts per cell (lead-acid)". For example, a 12-volt lead-acid battery having 6 cells with 1.2 volts/cell must not drop below 7.2 volts. A fully charged battery has an open circuit voltage of 12.6 volts. The voltage drop from 12.6 volts to 7.2 volts is 5.4 volts. Therefore, at 0.degree. F., the CCA of the battery is the current that the battery can supply and drop the voltage not more that 5.4 volts at the end of 30 seconds. For a 6-volt lead-acid battery, the maximum drop is 2.7 volts and for a 24-volt lead-acid battery, the maximum drop is 10.8 volts.
Using Ohm's law, the CCA is 5.4/R for a 12-volt battery 2.7/R for a 6-volt battery, and 10.8/R for a 24-volt battery, where R is the internal resistance of the battery.
The BCI CCA test is performed with a high amount of current for a long period of time (30 seconds) and at 0.degree. F. The battery's resistance changes over time throughout the 30-second test as the battery's charge is reduced. Therefore, if a small signal measurement of the battery's resistance is made and at a higher temperature, adjustments to the above formulas would have to be made. Experimental data shows that this adjustment is made by multiplying the constants in the above formulas by approximately two-thirds to give a CCA of 3.6/R for a 12-volt battery, 1.8/R for a 6-volt battery, 7.2/R for a 24-volt battery, were R is the internal resistance of the battery adjusted to approximately 70.degree. F. and full charge.